Answer:
{5}
Step-by-step explanation:
Set of counting numbers:
Set of numbers you count with, starting from 1. So
C = {1,2,3,4,5,....}
Proper subset of a set:
A proper subset of a set A is a subset B that is not equal to A, that is, all elements of B are in A but A has at least one element that is not in B.
In this question:
The set of counting numbers is C = {1,2,3,4,5,....}
Among the options, {-1,0,1} and {0} are not subsets of C, as they contain elements that are not in C, while {1,2,3,...} is not a proper subset, as it is equals to C. So the correct answer is {5}.
